Heretofore, floating cranes have been provided for building bridges, loading and unloading from docks, etc., which have typically included a rectangular barge structure upon which a crane structure is carried. Such rectangular barges typically range up to 200 feet in length and 50 feet in width, accommodating booms up to 300 feet in length. These structures have the disadvantage that the rectangular configuration and structure displaces a considerable amount of water requiring that a considerable amount of water be moved during maneuvers. When the crane boom swings laterally, the end of the barge loaded by the boom dips into the water placing side loads on the boom which, under certain severe conditions, can cause collapse of the boom. The resulting careening or listing of the barge to one side, as the boom swings, makes accurate positioning of the boom difficult and makes the whole structure out of level. Waves from natural causes or from passing of even a small yacht can cause considerable lift and side loading of the boom structure. Furthermore, the rectangular floating crane structure cannot be closely positioned to an obstacle during use since it is awkward and cannot be maneuvered in close without a dangerous likelihood of striking the obstacle.
Boom lengths have been limited on rectangular barges since the problems of maintaining the floating apparatus level and boom side loading increase with the length of the boom.